Sometimes when saving a game in multiplayer (cooperative) mode, all clients are thrown out. They can't rejoin the game immediatley but have to wait a short time before reconnecting works again.It seems that it happens more often if the clients are moving around or shooting while saving happens. However, I'm not sure what triggers the bug...

Sorry for the delay. I do not deal with multiplayer code much and initially left your report hoping that someone more familiar with that code would respond. As is, there is nothing I can do to help you. Running with -verbose output might help, but I am unsure whether that was ever written to pursue anything like this.

More precise steps to reproduce would be ideal. Failing that, quantifying the report might help. What is "thrown out"? I assume some specific error message appears. What does it say? How long do they need to wait to rejoin? If they voluntarily quit a game rather than being thrown out, are they able to rejoin more quickly than when they are thrown out? Are there any levels where this is particularly an issue? Have you played with these people on these levels in cooperative mode in 0.58.1 (that is, hold all variables the same other than Rebirth version)? If yes, did it exhibit the problem?

Does it ever occur other than when saving a game? What percentage of save attempts exhibit the problem? Is the game saved successfully such that you can restore it later? If yes, does immediately resaving after restore cause the problem again?